Endocrine Abstracts

A 38–year-old female was diagnosed with right breast cancer cT2mN0M0G3 with positive BRCA+ gene mutation. The patient was treated with neoadjuvant chemotherapy plus one dose immune checkpoint inhibitor Pembrolizumab following bilateral radical mastectomy, extirpation of the right sentinel lymph nodes and bilateral reconstruction with an implant. Approximately one month after using Pembrolizumab the patient noticed extreme fatigue, decreased blood pressure, accelerated pulse, weight loss of 4 kilograms. The blood test showed hyperthyroidism with thyroid stimulating hormone (TSH) <0.011 mU/l [reference range: 0.4 – 4.0], free thyroxine (FT4) – 34.6 pmol/l [reference range: 11.5 – 22.7] and free triiodothyronine (FT3) – 7.9 pmol/l [reference range: 3.5-6.5] without presence of anti-thyroid peroxidase and thyrotropin receptor antibodies. In addition, in blood test repeatedly was revealed adrenal insufficiency with cortisol 3.0 nmol/l [reference range: 166 – 507] and adrenocorticotropic hormone (AKTH) < 1.5 pg/ml [reference range: 7.2 – 63.3]. The therapy with Prednisolone 7.5 mg daily (5 mg in the morning and 2.5 mg in the afternoon) and Thiamazole 10 mg was started immediately. Three weeks after therapy initiation Thiamazole dose was reduced to 5 mg daily. After two more weeks the blood test showed hypothyroidism with TSH 9.7 mU/l [reference range: 0.4 – 4.0], FT4 – 11.1 pmol/l [reference range: 11.5 – 22.7] and Thiamazole was discontinued. The patient was observed, in three months with no medication thyroid hormones stabilized and no more therapy was needed in further observation period. Pituitary MRI showed no convincing indications of pathological changes in the pituitary gland. The therapy with prednisolone was continued in the same dose, a gradual improvement in clinical manifestations was observed. We hypothesize that immune checkpoint inhibitor Pembrolizumab caused permanent secondary adrenal insufficiency and transient hyperthyroidism.